The present invention relates generally to wireless networks and, particularly, the present invention relates to dynamic frequency and time slot detection and media access control in a non-frequency translating repeater.
Several emerging protocols and/or specifications for wireless local area networks, commonly referred to as WLANs, or wireless metropolitan area networks known as WMANs, are becoming popular including protocols such as 802.11, 802.16d/e, and related protocols also known by names such as “WiFi” or “WiMAX”, time division synchronization code division multiple access (TDS-CDMA), Personal Handy-phone Systems (PHS), and the like. Many of these protocols, such as PHS for example, are gaining popularity as a low cost alternative in developing nations for providing network access in a WMAN, or cellular-like infrastructure.
While the specifications of products using the above standard wireless protocols commonly indicate certain data rates and coverage ranges, these performance levels are often challenging to realize. Performance shortcomings between actual and specified performance levels can have many causes including attenuation of the radiation paths of RF signals, which for 802.16d/e is typically associated with a 10 MHz channel in the 2.3 to 2.4 GHz licensed band although 802.16 can support transmission frequencies up to 66 GHz. Of particular interest, due in part to its wide acceptance in the global market place, are systems such as PHS as noted above, which operate using a Time Division Duplex (TDD) protocol.
Problems arise in that structures such as buildings where wireless network support is desired may have floor plans including obstructing wall placements and the like, and may have construction based on materials capable of attenuating RF signals, all of which may prevent adequate coverage. Still further, data rates of devices operating using the above standard wireless protocols depend heavily on signal strength. As distances in the area of coverage increase, wireless system performance typically decreases. Lastly, the structure of the protocols themselves may affect the operational range.
Repeaters are commonly used in the wireless industry to increase the range of wireless systems. However, problems and complications arise in that system receivers and transmitters in any given device may, for example, in a TDD system operate within an allocated time slot. In such systems, when multiple transmitters operate simultaneously, as would be the case in repeater operation, difficulties may arise. Some TDD protocols provide defined receive and transmit periods and, thus, are resistant to collisions.
In a TDD system, receive and transmit channels are separated by time rather than by frequency and further, some TDD systems such as PHS systems and 802.16 systems, use scheduled times for specific uplink/downlink transmissions. Other TDD protocols such as 802.11 do not use scheduled time slots structured. Receivers and transmitters for TDD systems may be isolated by any number of means including physical separation, antenna patterns, frequency translation, or polarization isolation. An example of isolation using frequency translation can be found in International Patent Application No. PCT/US03/28558 entitled “WIRELESS LOCAL AREA NETWORK WITH REPEATER FOR ENHANCING NETWORK COVERAGE”, based on U.S. Provisional Application No. 60/414,888. It should be noted however, that in order to ensure robust operation, a non-frequency translating repeater in order to operate effectively must be capable of rapidly detecting the presence of a signal and operating cooperatively with the media access control and overall protocol associated with the TDD system in which it is repeating in order to effectively repeat the transmission on a timeslot.
A PHS system, as will be appreciated by one of ordinary skill in the art, is a TDD system with designated control timeslots for the uplink and the downlink on a designated frequency channel having a bandwidth of 300 KHz and a plurality of traffic time slots each of which may be assigned to another frequency carrier within a 20 MHz bandwidth. For each connection established within a PHS system, the uplink and downlink operate on the same frequency carrier and “channel”, however the uplink and downlink occupy different time slots. Of further interest are TDD systems operating under the 802.16 standards and protocols which, as will be appreciated, use a known frequency channel for all time slots.